11 research outputs found
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Strongly coupled, high-quality plasmonic dimer antennas fabricated using a sketch-and-peel technique
A combination of helium- and gallium-ion beam milling together with a fast and reliable sketch-and-peel technique is used to fabricate gold nanorod dimer antennas with an excellent quality factor and with gap distances of less than 6 nm. The high fabrication quality of the sketch-and-peel technique compared to a conventional ion beam milling technique is proven by polarisation-resolved linear dark-field spectromicroscopy of isolated dimer antennas. We demonstrate a strong coupling of the two antenna arms for both fabrication techniques, with a quality factor of more than 14, close to the theoretical limit, for the sketch-and-peel-produced antennas compared to only 6 for the conventional fabrication process. The obtained results on the strong coupling of the plasmonic dimer antennas are supported by finite-difference time-domain simulations of the light-dimer antenna interaction. The presented fabrication technique enables the rapid fabrication of large-scale plasmonic or dielectric nanostructures arrays and metasurfaces with single-digit nanometer scale milling accuracy. © 2020 Christoph Lienau, Martin Silies et al., published by De Gruyter, Berlin/Boston
Long-lived electron emission reveals localized plasmon modes in disordered nanosponge antennas
We report long-lived, highly spatially localized plasmon states on the surface of nanoporous gold nanoparticles-nanosponges-with high excitation efficiency. It is well known that disorder on the nanometer scale, particularly in two-dimensional systems, can lead to plasmon localization and large field enhancements, which can, in turn, be used to enhance nonlinear optical effects and to study and exploit quantum optical processes. Here, we introduce promising, three-dimensional model systems for light capture and plasmon localization as gold nanosponges that are formed by the dewetting of gold/ silver bilayers and dealloying. We study light-induced electron emission from single nanosponges, a nonlinear process with exponents of n approximate to 5...7, using ultrashort laser pulse excitation to achieve femtosecond time resolution. The long-lived electron emission process proves, in combination with optical extinction measurements and finite-difference time-domain calculations, the existence of localized modes with lifetimes of more than 20 fs. These electrons couple efficiently to the dipole antenna mode of each individual nanosponge, which in turn couples to the far-field. Thus, individual gold nanosponges are cheap and robust disordered nanoantennas with strong local resonances, and an ensemble of nanosponges constitutes a meta material with a strong polarization independent, nonlinear response over a wide frequency range
Fourier-transform spatial modulation spectroscopy of single gold nanorods
Sensing the scattered fields of single metallic nanostructures is a crucial step towards the applications of isolated plasmonic antennas, such as for the sensing of single molecules or nanoparticles. In the past, both near- and far-field spectroscopy methods have been applied to monitor single plasmonic resonances. So far, however, these spectral-domain techniques do not yet provide the femtosecond time resolution that is needed to probe the dynamics of plasmonic fields in the time domain. Here, we introduce a time-domain technique that combines broadband Fourier-transform spectroscopy and spatial modulation spectroscopy (FT-SMS) to quantitatively measure the extinction spectra of the isolated gold nanorods with a nominal footprint of 41×10 nm2. Using a phase-stable pulse pair for excitation, the technique is capable of rejecting off-resonant stray fields and providing absolute measurements of the extinction cross section. Our results indicate that the method is well suited for measuring the optical response of strongly coupled hybrid systems with high signal-to-noise ratio. It may form the basis for new approaches towards time-domain spectroscopy of single nanoantennas with few-cycle time resolution
The relationship between interhemispheric transfer time and physical activity as well as cardiorespiratory fitness in healthy older adults
The structural and functional degradation of the corpus callosum (CC) has been shown to play an important role in the context of cognitive aging (Reuter-Lorenz and Stanczak, 2000). This is also reflected by findings of elongated interhemispheric transfer time (IHTT) in older adults (Riedel et al., 2022). At the same time, a protective effect of physical activity (PA) and cardiorespiratory fitness (CRF) on brain health including the CC is widely accepted (Hillman et al., 2008; Loprinzi et al., 2020). Based on this idea, the present study investigated the relationship between IHTT and PA/CRF in 107 healthy older adults (m: 64, f: 43) aged 67.69 ± 5.18. IHTT was calculated detecting event-related potentials (ERPs) using an established Dimond-Task. PA was evaluated using accelerometry resulting in estimates of overall bodily motion and time spent at higher intensity PA. CRF was estimated using graded exercise testing, approximating running speed at 4 mmol/l blood lactate concentration. The results showed a negative correlation between IHT
Suppression of Radiative Damping and Enhancement of Second Harmonic Generation in Bull’s Eye Nanoresonators
We report a drastic increase of the
damping time of plasmonic eigenmodes
in resonant bull’s eye (BE) nanoresonators to more than 35
fs. This is achieved by tailoring the groove depth of the resonator
and by coupling the confined plasmonic field in the aperture to an
extended resonator mode such that spatial coherence is preserved over
distances of more than 10 μm. Experimentally, this is demonstrated
by probing the plasmon dynamics at the field level using broadband
spectral interferometry. The nanoresonator allows us to efficiently
concentrate the incident field inside the central aperture of the
BE and to tailor its local optical nonlinearity by varying the aperture
geometry. By replacing the central circular hole with an annular ring
structure, we obtain 50-times higher second harmonic generation efficiency,
allowing us to demonstrate the efficient concentration of long-lived
plasmonic modes inside nanoapertures by interferometric frequency-resolved
autocorrelation. Such a light concentration in a nanoresonator with
high quality factor has high potential for sensing and coherent control
of light-matter interactions on the nanoscale
Toward Plasmonics with Nanometer Precision: Nonlinear Optics of Helium-Ion Milled Gold Nanoantennas
Plasmonic nanoantennas are versatile
tools for coherently controlling
and directing light on the nanoscale. For these antennas, current
fabrication techniques such as electron beam lithography (EBL) or
focused ion beam (FIB) milling with Ga<sup>+</sup>-ions routinely
achieve feature sizes in the 10 nm range. However, they suffer increasingly
from inherent limitations when a precision of single nanometers down
to atomic length scales is required, where exciting quantum mechanical
effects are expected to affect the nanoantenna optics. Here, we demonstrate
that a combined approach of Ga<sup>+</sup>-FIB and milling-based He<sup>+</sup>-ion lithography (HIL) for the fabrication of nanoantennas
offers to readily overcome some of these limitations. Gold bowtie
antennas with 6 nm gap size were fabricated with single-nanometer
accuracy and high reproducibility. Using third harmonic (TH) spectroscopy,
we find a substantial enhancement of the nonlinear emission intensity
of single HIL-antennas compared to those produced by state-of-the-art
gallium-based milling. Moreover, HIL-antennas show a vastly improved
polarization contrast. This superior nonlinear performance of HIL-derived
plasmonic structures is an excellent testimonial to the application
of He<sup>+</sup>-ion beam milling for ultrahigh precision nanofabrication,
which in turn can be viewed as a stepping stone to mastering quantum
optical investigations in the near-field